Periglacial Structures in the Saskatchewan Gravels and Sands of Central Alberta, Canada

Abstract

The Saskatchewan gravels and sands are composed dominantly of quartzitic sandstones, chert, and arkosic sandstones, together with a few fragments of basic volcanic rock, limestones and bedrock of local derivation. They have been recognized widely throughout the plains of western Canada and northwestern United States, everywhere lying unconformably upon bedrock and invariably being covered by glacial drift. Ages from late Tertiary to early Pleistocene have been suggested for these gravels and sands. Near Edmonton, Alberta, temporary exposures in a gravel pit revealed structures in the Saskatchewan gravels and sands that are attributed to deformation by frost action. These structures are: (1) a zone of deranged pebbles, (2) involutions, and (3) fossil ice wedges, now full of sand. The conclusions drawn from this study are: (1) a periglacial climate existed in central Alberta before the arrival of the Keewatin ice that deposited the Wisconsin till; (2) the Saskatchewan gravels and sands discussed here were d...